[Flac] Exact metadata reproduction

[Josh Coalson]

--- Bryan Ford <baford at mit.edu> wrote:
[...]
> 	http://www.brynosaurus.com/pub/os/vxa.pdf

ooh, very cool.

> I've already integrated FLAC as an example media-type-specific
> compressor that 
> the archiver can use automatically on WAV files it runs across,
> rather than 
> futilely trying to run them through gzip or another general-purpose 
> algorithm.  It works, and everything's peachy, except for the minor
> problem 
> that FLAC is currently only lossless at the audio data level and not
> at the 
> file level.  I see that this issue has already been discussed on this
> list 
> and is in the FAQ, and for the current typical uses of FLAC I don't
> see its 
> current behavior as a problem.  But to work as a component of a 
> general-purpose archiver that's supposed to (by default anyway)
> reproduce the 
> files it archives _exactly_, we really need exact metadata
> replication for 
> whatever uncompressed audio formats it supports (certainly WAV,
> ideally 8SVX 
> too).
> 
> So, my question: has anyone done work on adding exact metadata
> replication 
> support to FLAC, or is it currently planned or on the horizon?

no, that's really outside the design goals of FLAC,
it will probably never be a WAVE file compressor.

but, for vxa you could develop a 'super-WAVE' format
for handling WAVE which on the encoder side splits a
WAVE file logically like so:

[RIFFWAVE.......]['data' subchunk][.....]

then uses a generic compressor to store the prefix
and suffix, and use libFLAC to compress the audio.

there are some other formats that are just WAVE
compressors, and these would solve the problem for
WAVE too but, you would still need a similar
super-AIFF format for AIFF, and so on, since there
are no such general compressors for those that I
know of.

so a general super-format system could be of wider
use.

as a hack, when dealing with 16-bit mono/stereo WAVEs,
you can feed the whole stream file to libFLAC as raw
samples and it will do almost as well.  this will
actually work for any file where the sample data is
aligned (e.g. 8 bit but probably not 20/24 bit).  e.g.
for a WAVE ripped from CD try:

flac --force-raw-format --endian=little --sign=signed
  --channels=2 --bps=16 --sample-rate=44100 file.wav

Josh



	
		
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